This invention relates to water treatment and in particular to the recycling or recirculation of used water in aquacultural facilities or other applications.
The invention removes dissolved and solid wastes from water and other fluids. In particular, in the aquacultural application it removes ammonia and other nitrogenous wastes, fecal material and uneaten food from the water. This treatment permits the water to be recycled and/or to meet legislated waste stream discharge criteria.
Many designs exist for filter equipment designed to remove dissolved and solid wastes. Biological filtration, the treatment of wastes by biological processes, is commonly used in filter designs. Plastic, or other materials, forms a media to provide substrata for the colonization of nitrifying bacteria. Submerged media designs suffer from channelling and clogging effects due to solids load and bacterial film sloughing. Trickling designs also suffer from channelling effects and often need to be very large because of the high void fraction of the media typically used. In northern climates, trickling designs are prone to super-chilling, which reduces capacity and freezing. Biological media are usually poor solids removal devices and require considerable operational expense. In addition, clogging and channelling destroys biological capacity and de-rates the filter.
Separation of solids from waste streams is accomplished by several processes and is very common. A common approach, related to this invention, is that of a swirl separator. The waste stream enters the unit and is induced to rotate. An overflow is designed to remove cleaned water in as quiescent a manner as possible. An underflow removes concentrated wastes. A major design problem is to achieve low velocities at the overflow to reduce transport of solids. Typical values are on the order of 90 cm/sec. In practice, these units rarely remove more than 70% of the solids in a typical waste stream. This, by itself, is unacceptable for water reuse, and an additional filter, usually a screen or sand filter, must be added.
A major problem with current technology is that several individual pieces of equipment are required to achieve the full desired effect. Typical swirl separators only remove solids and cannot treat dissolved wastes. Typical biological filters only remove dissolved waste and are sensitive to solids loading. It is difficult to optimize the overall design of the waste treatment system as the individual components are usually not well matched in performance and often come from several sources. Multiple units increase complexity, capital and operational expense and the tendency to failure of the system. In addition, most solids removal designs require periodic backflushing or other cleaning and cannot operate continuously unless equipped with automatic controls. Backflushing and cleaning of biological media is disruptive to the bacteria and de-rates the filter unit. PG,4